What are the side effects of oseltamivir?

Side Effects of Oseltamivir

The most common side effects of oseltamivir are nausea and vomiting, occurring in approximately 10% and 9% of adults respectively, with headache and skin reactions also reported; serious but rare adverse events include neuropsychiatric symptoms (particularly in adolescents), severe skin reactions, and hypersensitivity reactions including anaphylaxis. 1, 2

Common Side Effects

Gastrointestinal Effects

• Nausea and vomiting are the most frequently reported adverse events 3, 4
  • Adults: ~10% experience nausea without vomiting; ~9% experience vomiting (compared to 6% and 3% with placebo) 3
  • Children: 14% experience vomiting (vs 8.5% with placebo) 3, 4
  • Taking oseltamivir with food significantly reduces gastrointestinal side effects 5, 3, 2
  • Only 1% of patients discontinue treatment due to these symptoms 3
  • In real-world school outbreak settings, nausea/vomiting rates may be higher than clinical trials and can reduce compliance 3

Other Common Effects

• Headache 1, 2
• Skin reactions 1
• Diarrhea (particularly in children <1 year of age) 1
• Pain (when used for prophylaxis) 1

Serious Adverse Events (Rare but Important)

Neuropsychiatric Events

Transient neuropsychiatric events including self-injury, delirium, confusion, hallucinations, and abnormal behavior have been reported, predominantly in Japanese adolescents and adults 3, 4. However, multiple analyses found oseltamivir is NOT associated with increased risk of neuropsychiatric events 3. The FDA advises close monitoring for abnormal behavior during treatment 3, 4.

Key monitoring points:

• Watch for confusion, speech problems, shaky movements, seizures 2
• Monitor for hallucinations (hearing voices or seeing things that aren't there) 2
• Special attention required for adolescents and children 6
• Psychiatric symptoms may occur beyond 48 hours after starting treatment 6

Severe Skin and Allergic Reactions

Stop oseltamivir immediately and seek emergency care if any of these occur: 2

• Skin rash or hives
• Skin blistering and peeling
• Blisters or sores in mouth
• Swelling of face, eyes, lips, tongue, or throat
• Trouble breathing or chest pain/tightness
• Hypersensitivity reactions including anaphylaxis have been reported postmarketing 1

Hepatotoxicity

Recent evidence suggests potential liver toxicity:

• Fulminant hepatitis reported with ROR of 12.12 7
• Cases of acute hepatitis linked to oseltamivir therapy 8
• Increased liver inflammation and fibrosis markers in animal studies 9
• Monitor liver function carefully in patients with pre-existing liver disease 7, 8

Other Serious Events

• Seizures reported during postmarketing surveillance 4
• Ventricular fibrillation (ROR 7.68) 7
• Toxic epidermal necrolysis (ROR 7.21) 7
• Rhabdomyolysis (though more common with baloxavir) 7

Special Population Considerations

Infants and Young Children

• Limited safety data in children <1 year, but no age-related safety concerns demonstrated 3, 4
• Critical importance: careful attention to dosing to prevent errors 3, 4
• Use appropriate measuring devices (3-mL or 5-mL oral syringe for infants) 1

Pregnancy

• Pregnancy Category C medication 10
• Available information indicates oseltamivir does NOT increase risk of birth defects 2
• Passes into breast milk in small amounts 2

Renal Impairment

• Dose adjustment required for creatinine clearance 10-30 mL/min 4
• Not recommended for end-stage renal disease patients not on dialysis 2

Fructose Intolerance

• Oseltamivir suspension contains sorbitol and may cause stomach upset and diarrhea in fructose-intolerant patients 2

Clinical Pitfalls to Avoid

1. Don't dismiss gastrointestinal symptoms - While common, they can reduce compliance; always advise taking with food 5, 3, 2

2. Monitor beyond 48 hours - Psychiatric side effects may have delayed onset 6

3. Be vigilant with adolescents - Higher risk for neuropsychiatric events, particularly those with family history of psychiatric disorders 6

4. Watch for dosing errors in young children - Use appropriate measuring devices and double-check calculations 3, 4

5. Consider liver monitoring - Especially in patients with pre-existing liver disease or those on multiple medications 7, 8

6. Don't overlook hypersensitivity risk - Though rare, anaphylaxis can occur; educate patients on warning signs 1